Method of hardening steel



S. I. SALZMAN METHOD OF HARDENING STEEL Filed March 29. 1928 m mml Q 000OOOXOWW kk gmemloz Samue/ I. Sa/zman Patented Oct. 22, 1929- UNITED.STATES PATENT, ornca BAIUELI. BALM, OI BALTIMORE, MARYLAND KE'IHODHARDMG STEEL Application fled men 20, 1928. Serial no. 2 5,530.

- sired degree of elasticity, toughness, and capacity for resistingshock. p

A further object is to devise a method as above described, andparticularly one that is adapted for the hardening of thin steel, which.

is characterized by a high production rate, with a minimum of handlingon the part of the o erator.

A urther object is to devise a method of hardening thin steel sheets inthe form of razor blades which is designed to effect a substantiallyindividual treatment of the blades without preventing the attainment ofa favorable rate of manufacture.

A further object is to devise an apparatus for performing the hardeningor tempering steps of the method which is designed to-efiect thechilling of the heated steel with marked rapidity, while at the sametime absolutely preventing the creation of a warped cond1 tion throughinadequately relieving the internal strains.-

My improved method and the apparatus for efiectuatin I the same are moreparticularly intended oruse in the heat treatment of thin razor bladesof a well known ty As now practicedin the art, the blade lanks afterperforation and forming, are assembled in stacked and interleavedrelation on a frame with sheets having a high heat conductivity,

Y usually co' r. This assembly is then 4 blanks;

clamped, su ected to heat, and finally chilled to harden the bladeblanks, the copper sheets serving both to conduct heat inwardly to andoutwardly from the uncovered areas' of the Thepractice of the foregoingmethod prevents penetration of the blanks by oxidat1on,

' except over limited areas luring the heatin tain disadvantages whichdetract from its desirability for use. The stacking of the blades notonly requires undue time and labor, but the manifest difliculty ofuniformly clamping, heating, and cooling the blanks quickly at a uniformrate results in the production of blades having varying quahtiesl andcapacities for maintaining a cutting edge. The method and apparatusembodied in the present application are intended to conserve theadvantage of the older type of heat treatment in respect of preventingoxidation, while at the same time substantially effecting an individualtreatment of the blanks, thus satisfying the ideal requirements.Notwithstanding this advantage, the production rate is not lessened,owing to the improved mode of handling, and may in reality be increasedover existing methods. The product is characterized'by amarkeduniformityof structure, with a resulting capacity for withstandin shock andmaintaininga cutting edge over a onger period of time than now obtainsin the art.

For purposes of disclosure, the methodand apparatus are described withreference to the manufacture above noted, but it will be obvious thatapplication of the central idea in-- volved may be made with equalfacility to other products such as wire, springs of various types, andother articles reqmri treatment.

These and further objects of my inventionwill be set forth in thefollowing specification, reference being had to the accompanyng .heat

lized in carrying out my im roved method,

arranged in the order of then operation. Figs. 2, 3 and 4 aresectionstaken along lines of the same respective numerical desig- 85 ingdrawing, and the novel means by which nation in Fig. 1,.look-ing in thedirection of 1 A steel strip 10 of any desired length and having a widthand thicknessappropriate for thin razor blades is first perforated toform the usual openings 11 and 12, and is scored as at 13 to indicatethe end edges of the blades. These operations are performed prior to thehardening and the stripmay then be fed di' rectly to the apparatushereinafter described, or it may be wound on a spindle 14 in themanner-indicated by the numeral 15. From the spindle 14:, the strip 10is unwound and drawn through the various apparatus hereinafter describedby a pair pf coacting rollers 16, appropriately mounted and suitablydriven, between which said strip passes.

The first step in my improved method is the heating of the strip 10 to apredetermined temperature which is effected by passage through a tube 17of approved cross section which is arranged in a furnace 18 providedwith a burner 19. The strip 10 is propelled by the rollers 16 at apredetermined, constant speed and the furnace 18 is of a length adequateto insure the heating of the strip 10 to the desired temperautre beforeit issues therefrom.

Immediately adjacent the delivery opening of the tube 17 is arranged theapparatus for effecting the chilling of the heated strip for hardeningthe same. This apparatus comprises a pair of coacting chambers 20 and21, preferably arranged in vertical relation, with the strip 10 passingtherebetween and subjected to the weight of the upper casing 20.

' A chilling fluid 22 passes continually through said casings, ducts 23and 24-comn1unicatiug with the upper casing 20 for this purpose andducts 25 and 26 with the lower casing 21. Said casings are preferablyformed of a ma-- terial having a high heat conductivity, so that theheated strip 10 in passing therebetween will be quickly chilled, theabstracted heat being conducted to the chilling medium 22.

In order to relieve any internal strains that may be present in thestrip 10 after being subjected to the action of the chilling medium andto properly temper the same for insuring the obtention of a fine cuttingedge, said strip next passes between a pair of coacting channel frames27 and 28, also arranged in vertical relation, the bases of said framesserving to clamp said strip under the weight of the upper frame 27 andthe. upstanding sides thereof to properly confine the heat received fromburners 29 and 30. During passage between said frames, the strip will beagain heated, but to a temperature less than the initial temperaturereceivedin the furnace 18'.

After leaving this second heated zone, the strip 10 is again chilled bymoving between coacting casings 31 and 32 which are similarly arrangedand constructed to the casings 20 and 2 1. The heat treatment of thestrip 10 is then completed, after which it may be severed along thescored lines 13 to form the blade blanks which may then be ground'and"polished in any approved manner.

It will be observed that, according to my improved method, the heattreatment is' a continuous operation, thus insuring a high productionrate even though the, successive blade blank portions of the strip 10are treat ed individually. Two desirable, but heretofore conflictingcharacteristics, are therefore successfully combined. Heating andchilling of the strip 10 are effected without oxidation thereof orcontact with the flame or chilling medium and moreover, adequatepressure is maintained during the chilling and second heating operationto prevent warping of the strip. However, the latter pressure will notbe sufficiently great to prevent movement of the strip 10 by the rolls16 and this pressure may be exerted either in the manner shown, underthe action of gravity, or it may be effected mechanically, which wouldpermit the positioning of the chilling casings and heating frames inother position relations than vertical.

The product resulting from this mode of treatment possesses a highdegree of elasticity without affecting its capacity for receiving andmaintaining a cutting edge over a considerable period of time,characteristics which are highly desirable in razor blades. As beforestated, it is contemplated that the strip 10 will be propelled throughthe various steps of the tprocess by the rollers 16 at a constant rate 0dling has been found suitable for the heat treatment of razor blades,but it will be obvious that other types of products might requlre avarying or intermittent rate of speed.

While I have shown one set of elements and combinations thereof foreffecting my improved method and apparatus for the heat treatment ofsteel, it will be understood that the same are intended for the purposeof i1 lustration bnly and in nowise to restrict the same to the exactsteps and combinations shown, for many changes may be made thereinwithout departing from the spirit of my invention.

I claim:

1. The herein described method of hardening lengths of steel whichconsists in drawspeed, which mode of hanheated zone, a chilled zone, a.second heated zone including the application of heat to the oppositesides of said steel, and a second chilled zone to harden and temper theoriginal length progressively, a redetermined pressure being maintainedon t e portions of said steel passing through said chilled zones andsaid second heated zone, and said steel being maintained free fromcontact with the chilling medium employed.

In testimony whereof, I aflix my signature,

. AMUEL I. SALZMAN.

